The L-band Digital Aeronautical Communications System (LDACS), the worldwide first true integrated Communication, Navigation and Surveillance (CNS) system, is in the process of being standardized at the International Civil Aviation Organization (ICAO) and the Internet Engineering Task Force (IETF). The cellular system is considered a successor to the 30-years old Very High Frequency (VHF) Datalink mode 2 system (VDLm2) and intended for communications related to the safety and regularity of flight. With the initial rollout planned in the near future, the finalization of all its aspects, including security is of utmost importance. While previous works presented a cybersecurity architecture for LDACS, including a Public Key Infrastructure (PKI), certificates, a Mutual Authentication and Key Establishment (MAKE) procedure, as well as usage of established keys for protecting its user- and control-data plane, the protocol for secure LDACS handovers between cells has not been established. The objective of this work is to present a secure handover procedure for LDACS, fulfilling all security and performance requirements for data- and voice communications via LDACS.